KAGRA Logbook

LAS (General)

osamu.miyakawa - 17:34 Wednesday 22 October 2025 (35395)

Switching master laser

(Uchiyama, Miyakawa)

We swapped the master laser inside the box of neoLASE.

Preparation was done yesterday, so we started shutting down the power amplifier and confirmed the beam position on the camera. We shut down the master then, and loosen the screws to remove the aluminum board with the laser head. After removing the board, we kept the head position relatively using bars and clamps (Fig.1). After swapping the master head to another one, which was used in another neoLASE at Toyama Univ., we put the aluminum board with the new head into the box. However, we noticed that a big misalignment (~2 mm off at the EOM hole) had happened. It seems that some washers were used like a shim to adjust the angle of position of laser head, but it was too difficult to recover the same setting. So we decided to align using mirrors inside the box. This trial might destroy the alignment to the amplifier, but we had a recorded position on the camera, and we maximized the EOM transmissivity, then the beam reached the amplifier, and then we performed the fine alignment to the amplifier. Output power and PMC transmitted power became the same as before, with the same 6.4A. We measured the frequency noise of the neoLASE with the new master laser (Fig.2). It is a bit better than the orignal master at 1kHz but worse above 2kHz, and anyway worse than the FB laser.

We will see the long-term stability tonight. We keep PMC and IMC locked over the night.

Images attached to this report

35395_1761121888_SPEC_laser_freqnoise_fibervsNeoLASE20251022_cut.jpg

Comments to this report:

osamu.miyakawa - 8:41 Thursday 23 October 2025 (35398)

It seemed to be very stable for 16 hours last night!

Images attached to this comment

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osamu.miyakawa - 15:06 Thursday 23 October 2025 (35399)

(Uchiyama, Miyakawa)

We entered the PSL room and adjusted the laser crystal temperature to lock PLLs and to avoid mode-hop.

First, we changed the IR temperature from around 25 degrees to 38.7 degrees. This temperature was adjusted to the current green temperatures to lock the PLL, but the PMC transmitted power was fluctuating, and it indicated mode-hop of IR. We again changed the IR temperature to 39.3 degrees, and both green temperatures from 30.2 to 28.7 degrees for X and 27.2 to 25.8 degrees. IR temperature changed to higher, but it hopped to another mode, so the actual frequency got lower, and green temperatures were matched to the lower frequency.

Then we increased the IR current from 6.4A to 7.7A, which produces ~30W output power. We aligned the PMC again, and the transmissivity reached ~88.7%.

osamu.miyakawa - 9:09 Friday 24 October 2025 (35403)

There were 4 lock loss of IMC after working yesterday in 20 hours. 3 of 4 were kicked by seismic motion.

It seems to be not bad continuously.

Images attached to this comment

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osamu.miyakawa - 20:06 Friday 24 October 2025 (35406)

(Uchiyama, Miyakawa)

Ushiba-kun reported that GRY seemed to have mode hops, which introduced some fluctuation in the transmitted power of GRY.

We entered the PSL room and changed the crystal temperatures for all IR, GRX, and GRY. Yesterday, we had to reduce the temperature of both green by about 1.5 degrees in order to increase the temperature of IR by about 0.5 degrees. Today, we increased the IR temperature by 1.0 degree, from 39.4 to 40.4 degrees, and the greens followed: from 28.8 to 30.0 for X, and from 25.9 to 27.0 for Y. These green temperatures are close to the known values at which GRY and GRX had no mode hops.

During the afternoon check, Ushiba-kun reported that there seemed to be no mode hops in either of the green lights.